it is why you saw president obama warning assad so stride endly this week. >> and there has got to be so much discussion and intelligence circles as to why now what is prompting president assad to do this. the question really is what is that line? what is the trigger that would launch a potential u.s. military response? >> well, i think your first point is really key. why is assad even going down this route? why are his commanders going down this route? we have seen the fighting, our colleague, arwa damon has been talking about this for days, we have seen the fighting pick up around damascus. this is the center of power for the assad regime. and the fighting is quite intense around there. he is feeling the pressure. it is believed, of that fighting in and around the capital. so perhaps that's why he, number one, is supporting potentially this movement of chemical material. what the red line is, u.s. officials say, it moved a bit. it was any movement of chemical weapons. now it is really they're looking for the intent to use them. that, we're told, is what the u.s. is looking for now.